Quadrupole in which the pole electrodes comprise metallic rods whose mounting surfaces coincide with those of the mounting means

ABSTRACT

A quadrupole mass spectrometer is disclosed wherein the outwardly facing surfaces of elongated rods arranged in a rectangular array about a common space are of circular curvature in cross section having a radius of curvature conforming to the curvature of the inner surface of a plurality of ceramic cylinders having circular inner surface cross sections, axially enclosing and positioning the quadrupole rods.

I United States Patent Paul Michael Uthe Livermore, Calif. 701,745

Inventor Appl. No. Filed Jan. 30, 1968 Patented Jan. 5, 1971 Assignee UTI Mountain View, Calif. a corporation of California QUADRUPOLE IN WHICH THE POLE ELECTRODES COMPRISE METALLIC RODS WHOSE MOUNTING SURFACES COINCIDE WITH THOSE OF THE MOUNTING MEANS 7 Claims, 3 Drawing Figs.

U.S. Cl 250/419 Int. Cl H0lj 39/36 Field of Search ..250/41.9(E),

I, N, 3,153, R; 330/47; 250/4192 [56] References Cited UNITED STATES PATENTS 3,122,710 2/1964 Miller 3,128,432 4/1964 Gordon 3,410,997 11/1968 Brubaker....

Prin'zary Examiner-William F. Lindquist Assistant Examiner-C. E. Church Attorney-Limbach, Limbach & Sutton ABSTRACT: A quadrupole mass spectrometer is disclosed wherein the outwardly facing surfaces of elongated rods arranged in a'rectangular array about a common space are of circular curvature in cross section having a radius of curvature conforming to the curvature of the inner surface of a plurality of ceramic cylinders having circular inner surface cross sections, axially enclosing and positioning the quadrupole rods.

PATEN'TEU JAN" Slam 3. 5 53,451

DETECTOR 5-, h or; 08; (3% a (by dim mo: 52% 5g 03 v-g u on *2 III INVENTOR. P. MICHAEL UTHE BY WM/W ATTQRNEIYS QUADRUPOLE IN WHICH THE POLE ELECTRODES COMPRISE METALLIC RODS WHOSE MOUNTING SURFACES COINCIDE WITH THOSE OF TH MOUNTING MEANS This invention relates to new and improved quadrupole rods and rod mountings useful in quadrupole mass spectrometers.

In quadrupole mass spectrometers, a DC and superimposed RF voltage field established between a rectangular array of elongated rods is utilized to filter ions from an ion source according to the charge to mass ratio of the ions and thereby produce a mass spectrum of the ionized material at the output of an ion detector. Ideally, the inwardly facing surfaces of the elongated rods utilized in thdrectangular array should have hyperbolic curvature in cross section. Becauseof the expense in machining hyperbolic surfaces, circular rods are generally used, the inwardly facing surfaces of the rectangular array of rods providing a sufficiently accurate approximation'of the ideal hyperbolic surfaces. I

Precise positioning and placement of the quadrupole rods is critical to satisfactory operation and the extremely high voltcurate placement of the'rectangular array of rods while minimizing the machining requirements. Another object of the invention is to provide a quadrupole rod configuration which may be accurately mounted and positioned in a simple ceramic cylinder having a circular inner surface cross section.

Other objects, features and advantages of thepresent invention will become apparent in the following specification and accompanying drawings.

FIG. I is a cross-sectional view from the side of a quadrupole mass filter embodying the present invention and incorporated in aquadrupole mass spectrometer the remainder of which is shown as a block diagram. 7

FIG. 2 is a cross-sectional view of the quadrupole mass filter in the direction of the arrows on line 2-2 on FIG. 1 showing the configuration of quadrupole rods and a ceramic cylinder mounting.

-FIG. 3 is a fragmentary perspective view of the quadrupole rods and a ceramic cylinder mounting.

In the embodiment of the present invention illustrated in FIG. 1 there is provided a rectangular array of rods mounted in a plurality of ceramic cylinders 11 by screws 12 which pass through the ceramic cylinders to engage the rods 10. A DC voltage with an RF component superimposed thereon is fed from a power supply to opposing rods of the rectangular array through the input" contacts 13 which may also be screws.

Ions from an ion source 20 comprising an ionizer and electrostatic field lens are directed into the central region or common space enclosed by the quadrupole rods 10. Depending upon the field established between the'rectangular array of rods by the DC'and RF voltages, ions of only a certain charge to mass ratio travel the length of the rods undeflected into an ion detector 30. As the field between the rods is varied, the mass spectrum of the ionized material, and relative concentration ratios may be determined from the output of the ion detector.

A housing 14 may be provided for the quadrupole array and ceramic cylinders II.

As illustrated in FIG. 2, the inwardly facing surfaces 15 of the quadrupole rods may be of hyperbolic curvature in cross section or circular'curvatur'e in cross section. Generally, the

pie circular cross sections of uniform radius of curvature as formerly used in the art.

Though the outwardly facing surface 16 of each of the rods,

is provided with a circular curvature in cross section. the radius of curvature of the outwardly facing surface conforms to the curvature of the inner surface of the plurality of cylinders 11. By so forming the outwardly facing surfaces 16 of the quadrupole rods, i.e. the surfaces facing outwardly from the common elongate space enclosed by the rods, a simple ceramic mounting of cylindrical shape having a circular inner surface cross section may be utilized. The rods may thus be accurately positioned and secured to the axially enclosing ceramic cylinder mountings 11 by screws 12 as. shown in FIG. 3. Accurate machining of grooves, indentations, and protrusions on the ceramic mounting is thereby eliminated.

The radius of curvature of the outwardly facing surfaces of the rods is difierent from the radius of curvature of the inwardly facing surfaces of the rods and generally greater when rods having inner circular curvature are used. The inner surfaces however, may also be hyperbolic.

The rods may be made of molybdenum, stainless steel, or other similar material, while the ceramic cylinder mounting may be made of A1 05 or other similar nonconducting material.

The screws, not all of which are shown in the accompanying figures may be made of copper, stainless steel or other suitable material.

circular cross section is utilized being inexpensive and providing a sufficiently close approximation to the hyperbolic curvature. The entire surface of the rods, howevendo not have sim- I claim: 1

I. A quadrupole mass spectrometer of the type wherein a DC and superimposed RF field is established within an array of elongated rods mounted to receive ions from an ion source and selectively pass ions to an ion detector comprising: at least one mounting means of nonconductive material, each said mounting means having a passageway therethrough of circular cross section; a plurality of elongated metallic rods mounted in an array within the passageway of said mounting means about a common space the surface of each of said elongated rods facing outwardly from the common space having in cross section a circular curvature having a radius of curvature equal to the radius of curvature of the surface of the passageway through each of said mounting means, and means for securing said rods to said mounting means.

2. A quadrupole mass spectrometer as set forth in claim 1 wherein each said mounting means is formed of a ceramic material.

3. A quadrupole mass filter comprising a hollow cylindrical housing, at least one electrically insulating mounting means supported within said housing having an outside cylindrical surface comforming to the inside surface of said housing and a passageway therethrough of circular cross section, and a plurality of elongated metallic rods arranged in an array about a common space within said housing, said cylindrical mounting means axially enclosing said array of elongated rods, the surface of each of said elongated rods facing outwardly from the common space having a circular cross section of radius of curvature equal to the radius of curvature of the surface of the passageway through each said mounting means, and means for securing said rods to said mounting means.

4. A quadrupole mass filter as set forth in claim 3 whereirl the surface of each of said elongated rods facing toward the common space enclosed by said rods is circular in cross section.

5. A quadrupole mass filter as set forth in claim 3 wherein the surface of each of said elongated rods facing toward the common space enclosed by said rods is hyperbolic in cross 

1. A quadrupole mass spectrometer of the type wherein a DC and superimposed RF field is established within an array of elongated rods mounted to receive ions from an ion source and selectively pass ions to an ion detector comprising: at least one mounting means of nonconductive material, each said mounting means having a passageway therethrough of circular cross section; a plurality of elongated metallic rods mounted in an array within the passageway of said mounting means about a common space the surface of each of said elongated rods facing outwardly from the common space having in cross section a circular curvature having a radius of curvature equal to the radius of curvature of the surface of the passageway through each of said mounting means, and means for securing said rods to said mounting means.
 2. A quadrupole mass spectrometer as set forth in claim 1 wherein each said mounting means is formed of a ceramic material.
 3. A quadrupole mass filter comprising a hollow cylindrical housing, at least one electrically insulating mounting means supported within said housing having an outside cylindrical surface comforming to the inside surface of said housing and a passageway therethrough of circular cross section, and a plurality of elongated metallic rods arranged in an array about a common space within said housing, said cylindrical mounting means axially enclosing said array of elongated rods, the surface of each of said elongated rods facing outwardly from the common space having a circular cross section of radius of curvature equal to the radius of curvature of the surface of the passageway through each said mounting means, and means foR securing said rods to said mounting means.
 4. A quadrupole mass filter as set forth in claim 3 wherein the surface of each of said elongated rods facing toward the common space enclosed by said rods is circular in cross section.
 5. A quadrupole mass filter as set forth in claim 3 wherein the surface of each of said elongated rods facing toward the common space enclosed by said rods is hyperbolic in cross section.
 6. A quadrupole mass filter as set forth in claim 3 wherein said array of elongated rods comprises a rectangular array of four elongated rods.
 7. A quadrupole mass filter as set forth in claim 6 wherein said mounting means is formed in a cylindrical shape and is made of a ceramic material. 